1. Field of the Invention
The present invention relates to the memory function in a video processing apparatus such as a video camera and more particularly to a video apparatus with image memory function capable of realizing a plurality of functions using a memory such as the electronic enlarging processing and the recursive type noise reduction processing.
2. Description of the Related Art
A video apparatus (1) having the electronic enlarging function using a field memory, (2) having the recursive type noise reduction function using a field memory or (3) having the electronic enlarging function, the recursive type noise reduction function and a function selecting circuit to realize either one of the above functions by using a field memory has hitherto been developed as the video apparatus with image memory function.
As a typical example, the video apparatus having the electronic enlarging function using a field memory will first be described. (Japanese Patent Application No. 63-263207 (JP-A-2-109474), xe2x80x9cImage Memory Apparatusxe2x80x9d).
The video apparatus has a field memory having a capacity of storing an image of one field or more, a memory read control unit for reading a desired area of a signal of a first field stored in the field memory, and a memory write control unit for determining a write head address of a second field following the first field to be an address after an address next to a read end address of the area read by the memory read control unit.
With this construction, an input video signal is written to the field memory, starting with the write head address assigned by the memory write control unit, head and end addresses of a desired area to be read during a trailing field are determined, and the write head address is determined after an address next to the read end address. Through this, a video signal of the area to be read does not overlap a video signal to be newly written during the trailing field and the image enlarging processing can be realized with the memory of one field.
The video apparatus of the above construction, however, requires the field memory dedicated to realization of the electronic enlarging function and by using this field memory, it cannot afford to simultaneously realize the electronic enlarging function and the digital function using another field memory, for example, the recursive noise reduction function.
Next, the video apparatus having the recursive type noise reduction function using a field memory will be described. (xe2x80x9cA New Noise Reduction System for Video Cameraxe2x80x9d by Nakajima et al, IEEE Transactions on Consumer Electronics, Vol. 37, No. 3, August, 1991).
In the video apparatus, first subtraction means determines a difference signal between an input video signal and an output signal of a field memory. At that time, if the input video signal is a still image, then the video signal will hardly be contained in the difference signal and only a noise will be taken out. Second subtraction means subtracts this difference signal from the input signal, thereby reducing the noise.
With this recursive type noise reduction apparatus, however, the video signal is largely contained in the difference signal in the case of a moving picture. Consequently image degradation occurs, when the difference signal is subtracted from the input signal. Accordingly, on the statistical ground that the noise is generally smaller in amplitude than the signal, the difference signal is multiplied by a coefficient k, where 0xe2x89xa6kxe2x89xa61, by means of multiplier means and only a part of small amplitude is extracted as a noise. More specifically, for a part of the difference signal which is small in amplitude, the noise is extracted by controlling k to a value approximating 1 but for a part of the difference signal which is large in amplitude, the noise is extracted by controlling k to a value approximating 0. By subtracting the thus extracted noise from the input signal, the noise can be reduced while suppressing afterimage. By performing the control by the multiplier means based on the amplitude value in accordance with individual frequency bands of the input video signal, the noise reduction can be realized while further suppressing the afterimage.
The above construction, however, requires the field memory dedicated to realization of the recursive type noise reduction function and by using this field memory, it cannot afford to simultaneously realize the recursive type noise reduction function and the digital function using another field memory, for example, the electronic enlarging function.
Finally, the video apparatus having the electronic enlarging function, the recursive type noise reduction function and a function selecting circuit to realize either one of the above functions by using a field memory will be described. (Japanese Patent Application No. H4-44690 (JP-A-6-46317) entitled xe2x80x9cVideo Signal Processing Circuitxe2x80x9d and U.S. Pat. No. 5,345,264 entitled xe2x80x9cVideo Signal Processing Circuit for a Video Camera Using a Luminance Signalxe2x80x9d).
In a video signal processing circuit having a memory for storing at least one field of an output resulting from AD conversion of a CCD output, a memory control circuit for controlling the read position of the memory in accordance with a designated zoom magnification, and an interpolation circuit for interpolating the output of the memory with an interpolation coefficient in accordance with the zoom magnification, the memory is also used as a memory constituting a recursive type noise reducer. Also, in a video signal processing circuit having a memory for storing at least one field of an output resulting from AD conversion of a CCD output, a moving vector detecting circuit for detecting a moving vector from the AD converted output, a memory control circuit for controlling the position of reading of the memory in accordance with a moving vector specified on the basis of the output of the moving vector detecting circuit or a designated zoom magnification, and an interpolation circuit for interpolating the output of the memory with an interpolation coefficient complying with a zoom magnification, the memory is also used as a memory constituting a recursive type noise reducer.
In the above construction, however, realization of the recursive noise reduction function and the electronic type enlarging function is switched using the provided field memory and both the functions cannot be realized simultaneously.
A principal object of the present invention is to provide a video apparatus with image memory function which can simultaneously realize a plurality of functions such as the electronic enlarging function and the recursive type noise reduction function by using a memory of one field.
To accomplish the above object, a video apparatus with image memory function according to the present invention comprises a field memory having at least two independent read ports and a capacity of storing an image of one field or more, at least two memory read control units corresponding to the two independent read ports, and a memory write control unit.
In the present invention, a first read control unit standing for one of the at least two read control units reads a first area standing for a desired area of a signal of an n-th field stored in the field memory, a second read control unit standing for the other of the at least two read control units reads a second area standing for an area which contains the first area of the signal of the n-th field stored in the field memory and is wider than the first area, a write head address of an (n+1)-th field following the n-th field is so determined as to be after an address next to a read end address of the first area, a video signal of the (n+1)-th field is written to the field memory, starting with the write head address, and the signal of the first area is delivered as a video signal.